The invention relates to a method for operating a collision avoidance or collision mitigation system of a vehicle and to a collision avoidance or collision mitigation system.
Systems for distance and speed control are widely known, which not only intervene in a braking maneuver in a case of doubt, but also can predict rear end collisions and, as a result, minimize the risk for the passengers. In such so-called “collision mitigation systems” (CMS), all necessary countermeasures are already initiated automatically before a possible collision with a potential collision object. Thus, the known CMS calculates the probability of a collision on the basis of driving conditions, distance from the preceding vehicle and relative speed. If necessary, the CMS then independently intervenes in order to prevent collisions. The timing for this system intervention is based on a necessary nominal delay and on a driver reaction time. Before the system intervention, a visual and/or audible warning function is activated in the known CMS. However, there is no additional safety function for the vehicle driver in this system.
German patent document DE 44 11 184 C2 discloses a controllable belt pretightener, which is effective only up to a certain pretensioning force before the collision, as safety function against a possible collision of a vehicle with a collision object. In the case of an actual collision, a second belt tightener with increased tensioning force is provided.
One object of the invention is to provide an improved collision avoidance or collision mitigation system for a vehicle, and a method of operating such a system.
This and other objects and advantages are achieved by the method according to the invention, in which an existing driving space between a vehicle and a potential collision object is detected and a first warning function and/or information function is activated when a first threshold value is reached. A system intervention with autonomous partial braking combined with at least one further safety measure is implemented when a second threshold value is reached. As a result, the collision avoidance system becomes much safer because, apart from the warning functions already known, partial braking is provided even before the actual system intervention, according to the invention. At the same time, the vehicle driver is additionally warned by the active safety function combined with the partial braking in a more time-critical situation.
As a first warning function and/or information function, for example, audible warning signals (e.g., conspicuous tones/sounds, voice outputs or also recommendations for actions) or visual warning signals (e.g., light signals) can be delivered. Furthermore, it is also possible to provide visual warning signals, such as visual instructions for actions on the display, or representations of the vehicle and of the obstacle on the display, or haptic warning signals (for example vibrations or rattling of the steering wheel). A haptic warning signal can also be belt pulling, which alerts the vehicle driver particularly urgently to an impending hazard situation.
As a further safety measure, fastening of passengers, designed as a safety function, for example in the form of belt tightening, can preferably take place. The partial braking and the belt tightening not only warn the vehicle driver, but also reduce the crash energy, even before a driver reaction.
In a preferred embodiment of the invention, the autonomous braking intervention can be reduced to a value which is below a deceleration required to collision avoidance. This has the advantage that the collision avoidance system cannot be misused as “distance assistant” but that the avoidance of a possible collision presupposes a degree of alertness of the vehicle driver. The partial braking can be carried out, for example, with a braking acceleration of about maximally 90% of the deceleration required for collision avoidance.
In addition, the braking acceleration of the partial braking is advantageously maintained below a maximum limit predetermined in dependence on speed. At low driving speeds, a higher limit can thus be set for the braking acceleration than with higher driving speeds. For example, a braking acceleration of −4 m/s2 can be set as a limit at a driving speed of up to about 50 km/h, a braking acceleration of −3 m/s2 at a driving speed of about up to 150 km/h and a braking acceleration of −2 m/s2 at a driving speed of about up to 250 km/h.
According to the invention, the system intervention for collision avoidance or collision mitigation can be designed as autonomous braking intervention and/or as autonomous steering intervention which can be deactivated on demand by a vehicle driver. For example, the system intervention can be deactivated by an emergency braking triggered by the vehicle driver. It can also be provided that a threshold value calculated from brake pedal travel and brake pedal speed is determined for the deactivation of the system intervention, for example when at least 50% of the pedal travel is reached.
In an improved system, short or fast braking events can be intercepted such as, for example, those shortly before overtaking when the vehicle driver approaches a vehicle ahead and the passing lane is not free yet. An exit from system intervention can also be achieved by an acceleration triggered by the vehicle driver and/or by high steering dynamics (for example strong or fast steering wheel deflections). When system intervention is deactivated, only the audible and/or visual distance warning suitably occurs. The collision avoidance or collision mitigation system can thus be intuitively deactivated if the driver chooses alternative collision avoidance by giving gas, reducing the braking or by steering. The coordinated collision warning which is based on identical criteria in each case advantageously provides a continuous uniform system.
The invention also relates to a collision avoidance or collision mitigation system for a vehicle, which includes sensors for detecting the environment, for example in the form of a radar, a lidar (light detection and ranging), a video sensor and/or an ultrasonic sensor as means for detecting an existing driving space between the vehicle and the potential collision object. The environmental sensors are particularly preferably constructed as 77-GHz radar sensors which can advantageously have a range of between about 7 and 150 m with an aperture angle of approx. 9°.
In an alternative embodiment, two 24-GHz radar sensors which in each case can have a range of about 0.1 to 30 m at an aperture angle of approx. 45° can be constructed alternatively or additionally. The use of these sensors advantageously achieves a higher object quality than in the case of a known vehicle interval controller with the same sensor configuration. Although the same objects are advantageously detected in this manner standing objects can also be observed; such objects frequently are not detected by conventional sensors, or can be detected too often or wrongly. According to the invention, with the given objective of higher object quality, the risk of mistriggerings or wrong triggerings can be reduced in fact, for example, the reaction of the vehicle driver is also utilized for recognizing a situation.
Using the sensors provided, the objects can be seen for a long time and reliably even on curvy roads full with multiple lanes. Due to the narrower lane requirements achieved by using these sensors, for example, drivers cutting in can be admitted later and drivers moving out can be released earlier. Furthermore, standing objects can be advantageously taken into consideration if they have previously moved. For example, it is possible to take into consideration a vehicle which is stopped at a traffic light and which has been continuously detected before stopping, or an immobile object whose own speed is less than about 72 km/h can be taken into consideration if it has previously been detected particularly reliably by the sensor. Overall, the sensor system advantageously provides for a reliable interpretation and intelligent situation analysis even in the case of critical scenarios.
In the case of hazard of wrongly positioned objects or of soiling, the reliability of the sensors can reach its limits.
The environment-detecting sensors supply the necessary information for detecting the actual state of the situation around the vehicle. Using the environment-detecting sensors, distance values between the vehicle and obstacles in the environment of the vehicle are calculated. In this process, the relevant potential collision object is selected and evaluated for an instantaneous collision hazard by means of the “time-to-avoid” and “time-to-brake” criteria. “Time-to-avoid” comprises a period which remains for the vehicle driver to subsequently prevent a collision with the potential collision object by means of an evasion maneuver, and “time-to-brake” comprises a period which remains to the vehicle driver for subsequently preventing a collision with a potential collision object by means of a braking maneuver. By means of these factors, in conjunction with the data recorded by the environment-detecting sensors, a situation evaluation can be produced by means of which accident-critical situations can be accurately predicted.
The collision avoidance or collision mitigation system according to the invention is advantageously activated on the basis of the situation evaluation and a vehicle status interpretation. The vehicle status interpretation can be used for detecting an instantaneous vehicle status for which purpose a distance warning function of a known vehicle interval controller is used. The vehicle interval controller recognizes a preceding vehicle by radar and detects its distance and speed. As soon as the sensors signal clear track ahead, the vehicle automatically accelerates up to the traveling speed desired by the vehicle driver. The vehicle interval controller can thus predictively select the appropriate speed in the traffic flow and adapt it to the respective situation. In this arrangement, the vehicle interval controller can always maintain the appropriate distance from the preceding vehicle.
The method according to the invention advantageously activates a safety function in addition to the known vehicle interval controller function. In this arrangement, an analytical controller can output a value for a nominal delay required for collision avoidance, which is calculated by means of a distance between the vehicle and the potential collision object and a relative speed. The relative speed is the speed at which the vehicle is approaching the potential collision object.
Overall, the activated collision avoidance or collision mitigation system provides a particularly advantageous graded safety function which can be intuitively deactivated depending on the reaction of the vehicle driver. If the vehicle driver brakes independently, there is advantageously a transition to the autonomous braking assistance system, developed in accordance with the invention, which is carried out in conjunction with the further safety measure, for example belt tightening.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.